Monophyly for the Nematodirinae, with 5 genera, Murielus, Rauschia, Nematodiroides, Nematodirus, and Nematodirella was confirmed based on comparative morphology and phylogenetic analysis of structural characters. This concept for the nematodirines excludes the monotypic Lamanema chavezi, but otherwise corroborates generic-level diversity as defined in prior studies. Exhaustive analysis resulted in 1 most parsimonious tree (36 steps; consistency index [CI] = 0.94; retention index [RI] = 0.93; excluding phylogenetically uninformative characters, CI = 0.92). As an inclusive or monophyletic group, Nematodirinae was diagnosed by 8 synapomorphies (7 are unequivocal): (1) large eggs, (2) long filiform spicules, (3) basal division of the dorsal ray, (4) symmetrical membrane enveloping the spicule tips, (5) fused structure of the spicule tips, (6) absence of the gubernaculum, (7) development of the third-stage larva within the egg, and (8) ornamentation in the form of discrete bosses on the bursa. Exclusion of Lamanema will require new assessments of historical biogeography and the evolution of host associations for the nematodirines.